<div class="main-background-top"></div>
<div class="main-background-bottom"></div>
<script type="text/javascript">
	var bodyHeight = jq('.main-background-body').height()
	var mainHeight = jq('.main-content').height()
	var bgHeight = 0
	var bottompadding = jq('.main-background-body').attr('bottompadding')
	bgHeight = bodyHeight - jq('.main-background-top').height() - parseInt(bottompadding?bottompadding:0)
	jq('.main-background-bottom').height(bgHeight)
</script>